Propylene polymers are obtained by homopolymerization of propylene or copolymerization of propylene and other olefins in the presence of a so-called Ziegler-Natta catalyst mainly composed of a solid catalyst component containing titanium and an organoaluminum compound. Known polymerization techniques include polymerization in the presence of an inert hydrocarbon solvent, polymerization in liquefied propylene, and polymerization in a gaseous phase in the substantial absence of an inert solvent .or liquefied propylene.
However, in the production of propylene-olefin random or block copolymers, a considerably large proportion of amorphous polymers is by-produced, and the resulting polymer particles have poor fluidity and a reduced bulk density due to their surface tackiness. In an extreme case, the particles adhere to various equipment such as a reaction vessel and a hopper, stop flowing due to bridging, or undergo agglomeration or caking.
The production of propylene polymers, especially random or block copolymers, has thus been under restrictions arising from the above-described poor powder properties such that the copolymerization ratio of other olefins (the amount of other olefins in the copolymer) should be limited. The gaseous polymerization method is considered to slightly alleviate such disadvantages but is still unsatisfactory.
Furthermore, in the production of block copolymers, adhesion of polymer particles to the inner wall of reactors and caking of the particles not only are a great hinderance to stable operation but deteriorate the product quality.